Rotary magnetically operated valves are well known, one such valve being disclosed in Canadian Patent No. 1,092,589 issued on Dec. 30, 1980 to Nova Scotia Research Foundation Corporation. Such a valve is used to control the flow of a substance such as a liquid or a gas, the valve having particular value when the fluid flowing therethrough is hazardous due to toxicity, radiation or corrosion. The valve of the Canadian patent has its valve member, e.g. a butterfly, attached to a valve stem which is rotatable on a rotation axis and which is also attached to a carrier. The carrier mounts a plurality of rare earth magnets about its outer periphery, with adjacent magnets having alternate polarity. The carrier is enclosed by a barrier member which is hermetically sealed to the valve body so that hazardous material passing through the valve is always contained within the barrier member and the valve body.
Externally of the barrier is another carrier, usually annular in shape, this carrier mounting another plurality of rare earth drive magnets about the internal circumference thereof, these magnets also being of alternating opposite polarity. A suitable means such as a handle, valve actuator or lever arm is provided to effect rotary movement of the drive carrier relative to the stationary barrier. Magnetic interaction across the barrier member causes the internal driven carrier to follow the rotary movement of the external drive carrier so that the valve member is rotated to progressively open or close the valve. Rotation limit means can be provided to prevent the valve member from rotating too far in the valve body.
Valves in accordance with the above patent are able to handle heavy flow volumes and the size of the valve member can be very large inasmuch as the magnetic drive can produce high torques. On occasion, however, a valve may jam and the torque available magnetically is not sufficient to overcome the jam. It is therefore imperative that there be some mechanism available to override the magnetic operation of the valve so that the valve can be either opened or closed by hand until such time as the fault which caused the jam can be rectified. Usually the fault is such that the valve must be dismantled, repaired, and rebuilt; otherwise there would have been no problem in the first place.